All-solid-state secondary battery and method of charging the same

ABSTRACT

An all-solid-state secondary battery including: a cathode including a cathode active material layer; an anode including an anode current collector, and an anode active material layer on the anode current collector, wherein the anode active material layer includes an anode active material which is alloyable with lithium or forms a compound with lithium; and a solid electrolyte layer between the cathode and the anode, wherein a ratio of an initial charge capacity (b) of the anode active material layer to an initial charge capacity (a) of the cathode active material layer satisfies a condition of Equation 1: 0.01&lt;(b/a)&lt;0.5, wherein a is the initial charge capacity of the cathode active material layer determined from a first open circuit voltage to a maximum charging voltage, and b is the initial charge capacity of the anode active material layer determined from a second open circuit voltage to 0.01 volts vs. Li/Li + .

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.18/163,963, filed on Feb. 3, 2023, which is a continuation of U.S.patent application Ser. No. 17/208,142, filed on Mar. 22, 2021, andissued as U.S. Pat. No. 11,764,407, which is a continuation of U.S.patent application Ser. No. 16/196,252, filed on Nov. 20, 2018, andissued as U.S. Pat. No. 10,985,407, which claims priority to and thebenefit of Japanese Patent Application No. 2017-223661, filed on Nov.21, 2017, in the Japanese Patent Office, and all the benefits accruingtherefrom under 35 U.S.C. § 119, the contents of each of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to an all-solid-state secondary battery,methods of manufacture thereof, and methods of charging the same.

2. Description of the Related Art

Recently, all-solid-state secondary batteries using a solid electrolyteas an electrolyte have attracted attention. To increase energy densityof an all-solid-state secondary battery, use of lithium as an anodeactive material has been proposed. The theoretical specific capacity(i.e., the capacity per unit mass) of lithium is 3,861 milliampere-hoursper gram (mAh/g), which is about 10 times greater than that of graphite,which has a theoretical specific capacity of 372 mAh/g. Also, lithiumprovides a capacity density of 2062 milliampere-hours per cubiccentimeter (mAh/cm³), which is about three times greater than thecapacity density of graphite, which provides 756 mAh/cm³. Thus, whenlithium is used as an anode active material, an all-solid-statesecondary battery may be lighter and smaller than a lithium ion batteryhaving a graphite anode active material. Also, a lithium battery havinggreater rate capability may be realized.

However, when lithium is used as an anode active material in anall-solid-state battery a lithium dendrite may form, which may causereduced in capacity, or a short circuit. There accordingly remains aneed for an improved anode active material and methods providing theimproved anode active material.

SUMMARY

An aspect of the present disclosure is made to address theabove-described problems, and provides an all-solid-state secondarybattery that uses lithium as an anode active material and may haveenhanced characteristics, and a method of charging the same.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an embodiment, an all-solid-state secondary batteryincludes: a cathode including a cathode active material layer; an anodeincluding an anode current collector, and an anode active material layeron the anode current collector, wherein the anode active material layerincludes an anode active material which is alloyable with lithium orforms a compound with lithium; and a solid electrolyte layer between thecathode and the anode, wherein a ratio of an initial charge capacity ofthe anode active material layer to an initial charge capacity of thecathode active material layer satisfies the condition of Equation 1:

0.01<(b/a)<0.5  Equation 1

-   -   wherein a is the initial charge capacity of the cathode active        material layer determined from a first open circuit voltage to a        maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer        determined from a second open circuit voltage to 0.01 Volts (V)        vs. Li/Li⁺.

In this regard, the initial charge capacity of the cathode activematerial layer is greater than that of the anode active material layer.In addition, the anode active material layer may include a materialalloyable with lithium or forming a compound with lithium. When theall-solid-state secondary battery having such a configuration ischarged, lithium may be incorporated into the anode active materiallayer at the initial stage of charging. After the initial chargecapacity of the anode active material layer is exceeded, lithium isdeposited on a rear surface of the anode active material layer. A metallayer may be formed by the deposited lithium. During discharge, lithiumof the anode active material layer and the metal layer may be ionizedand transferred towards the cathode. Because lithium may be used as ananode active material, energy density may be enhanced. In addition, theanode active material layer may cover the metal layer, and thus may actas a protective layer for the metal layer, and also the anode activematerial layer may inhibit the deposition and growth of a dendrite. Thismay inhibit or reduce the likelihood of a short circuit and capacityreduction of the all-solid-state secondary battery, and furthermore, mayenhance characteristics of the all-solid-state secondary battery.

The anode active material layer may include the anode active materialand a binder.

In this regard, the anode active material layer may be stabilized on theanode current collector. For example, when the anode active materiallayer does not include a binder, the anode active material layer maydetach from the anode current collector. A portion of the anode currentcollector, from which the anode active material layer may be detached,is exposed, and thus a short circuit may occur. The anode activematerial layer may be formed by, for example, coating a slurry, in whichmaterials constituting the anode active material layer are dispersed,onto an anode current collector and drying the coated anode currentcollector. The binder may be included in the anode active material layerto stably disperse the anode active material in the slurry. As a result,when the slurry is coated onto the anode current collector by, forexample, screen printing, clogging of a screen (e.g., clogging of ascreen due to an aggregate of the anode active material) may beminimized or suppressed.

An amount of the binder may range about 0.3 weight percent (wt %) toabout 15 wt %, with respect to a total weight of the anode activematerial layer.

In this case, the all-solid-state secondary battery has further enhancedcharacteristics.

The anode active material layer may have a thickness of about 1micrometer (μm) to about 20 μm.

The anode active material may be in the form of a particle, and anaverage particle diameter D50 of the anode active material may be about4 μm or less.

The anode active material may include at least one of amorphous carbon,gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag),aluminum (Al), bismuth (Bi), tin (Sn), or zinc (Zn).

The anode active material may include amorphous carbon.

The anode active material may include a mixture of the amorphous carbonand at least one of Au, Pt, Pd, Si, Ag, Al, Bi, Sn, or Zn.

The anode active material may include a mixture of a first particlecomprising amorphous carbon and a second particle comprising a metal, asemiconductor, or a combination thereof, wherein an amount of the secondparticle may range from about 8 wt % to about 60 wt %, with respect to atotal weight of the mixture.

The all-solid-state secondary battery may further include a thin filmdisposed on the anode current collector, the thin film including anelement alloyable with lithium. The thin film may be arranged betweenthe anode current collector and the anode active material layer.

The thin film may have a thickness of about 1 nanometer (nm) to about500 nm.

The all-solid-state secondary battery may further include a metal layerdisposed between the anode current collector and the anode activematerial layer, wherein the metal layer may include lithium, a lithiumalloy, or a combination thereof.

The metal layer may be formed between the anode current collector andthe anode active material layer before the all-solid-state secondarybattery is charged.

In an embodiment wherein the metal layer is formed between the anodecurrent collector and the anode active material layer before theall-solid-state secondary battery is charged, the metal layer may beprepared before the first charge cycle. Since the metal layer acts as alithium reservoir, the all-solid-state secondary battery has furtherenhanced characteristics.

The metal layer may have a thickness of about 1 μm to about 200 μm.

The anode current collector, the anode active material layer, and aregion therebetween may be Li-free regions at an initial state of orafter discharge of the all-solid-state secondary battery.

The all-solid-state secondary battery may be a lithium battery.

According to another embodiment, an all-solid-state secondary batterymay include a cathode; an anode; and a solid electrolyte layer, whereinthe cathode includes a cathode active material layer, wherein the anodeincludes an anode current collector and an anode active material layeron a surface of the anode current collector, wherein the anode activematerial layer comprises a binder and an anode active materialcomprising amorphous carbon, wherein the solid electrolyte layer isbetween the cathode active material layer and the anode active materiallayer, and wherein a ratio of an initial charge capacity of the anodeactive material layer to initial charge capacity of the cathode activematerial layer satisfies the condition of Equation 1:

0.01<(b/a)<0.5  Equation 1

-   -   wherein a is the initial charge capacity of the cathode active        material layer, determined from a first open circuit voltage to        a maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer,        determined from a second open circuit voltage to 0.01 V vs.        Li/Li⁺.

The amorphous carbon may include furnace black, acetylene black, Ketjenblack, thermal black, channel black, lampblack, graphene, or acombination thereof.

The amorphous carbon may be in a form of a particle and may include anaverage particle diameter D50 of about 4 micrometers or less.

The anode active material may further include a second particle.

A ratio of the amorphous carbon to the second particles may be about20:1 to about 1:2, or about 10:1 to about 1:1.

The second particle may include silicon, silver, tin, zinc, platinum, ora combination thereof.

The second particle may include silver, tin, zinc, or a combinationthereof.

The binder may include styrene butadiene rubber,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or acombination thereof.

The all-solid-state secondary battery may further include a thin filmdisposed on the anode current collector and between the anode currentcollector and the anode active material layer, the thin film including alithium compound or an element alloyable with lithium.

The ratio of the initial charge capacity of the anode active materiallayer to the initial charge capacity of the cathode active materiallayer may satisfy a condition of Equation 1A:

0.01<(b/a)<0.3  Equation 1A

-   -   wherein a is the initial charge capacity of the cathode active        material layer, determined from a first open circuit voltage to        a maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer        determined from a second open circuit voltage to 0.01 V vs.        Li/Li⁺.

The ratio of the initial charge capacity of the anode active materiallayer to the initial charge capacity of the cathode active materiallayer may satisfy Equation 1B:

0.01<(b/a)<0.2  Equation 1B

-   -   wherein a is the initial charge capacity of the cathode active        material layer, determined from a first open circuit voltage to        a maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer,        determined from a second open circuit voltage to 0.01 V vs.        Li/Li⁺.

The ratio of the initial charge capacity of the anode active materiallayer to the initial charge capacity of the cathode active materiallayer may satisfy a condition of Equation 1C:

0.01<(b/a)<0.1  Equation C

-   -   wherein a is the initial charge capacity of the cathode active        material layer, determined from a first open circuit voltage to        a maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer,        determined from a second open circuit voltage to 0.01 V vs.        Li/Li⁺.

According to still another embodiment, a method of charging theall-solid-state secondary battery includes charging the all-solid-statesecondary battery, wherein the initial charge capacity of the anodeactive material layer is exceeded.

A charge capacity of the all-solid-state secondary battery may be abouttwo times to about 100 times greater than the charge capacity of theanode active material layer.

At an initial charge, lithium may be incorporated into the anode activematerial layer. After the initial charge capacity of the anode activematerial layer is exceeded, lithium may be deposited on a rear surfaceof the anode active material layer between the anode active materiallayer and the anode current collector to form a lithium metal layer onthe current collector. During discharge, the lithium of the anode activematerial layer and the lithium metal layer may be ionized andtransferred to the cathode. Thus, the lithium metal layer may be used asan anode active material. In addition, since the anode active materiallayer covers the lithium metal layer, the anode active material layermay act as a protective layer for the metal layer and may suppress thedeposition and growth of a dendrite, thereby inhibiting a short circuitand avoiding capacity reduction of the all-solid-state secondarybattery.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view illustrating a firstembodiment of a structure of an all-solid-state secondary battery;

FIG. 2 is a scanning electron microscope (SEM) image of a cross-sectionof an all-solid-state secondary battery after overcharging an anodeactive material layer;

FIG. 3 is a schematic cross-sectional view illustrating a secondembodiment of an all-solid-state secondary battery;

FIG. 4 is a schematic cross-sectional view illustrating an embodiment ofa structure of a second embodiment of an all-solid-state secondarybattery;

FIG. 5A is an SEM image of a cross-section of an all-solid-statesecondary battery in which graphite was used as an anode activematerial;

FIG. 5B is an SEM image of a cross-section of an all-solid-statesecondary battery in which scaly graphite was used as an anode activematerial;

FIG. 6 is a graph of specific capacity (milliampere hours per gram,mAh/g) versus discharge current density (milliamperes per squarecentimeter, mA/cm²) showing output characteristics when using an anodeactive material comprising furnace black and silver (Ag);

FIG. 7 is a graph of specific capacity (mAh/g) versus discharge currentdensity (mA/cm²) showing output characteristics when using an anodeactive material comprising furnace black anode and silicon (Si), tin(Sn), or zinc (Zn);

FIG. 8 illustrates an embodiment of a method of charging anall-solid-state secondary battery;

FIG. 9 is a graph of voltage (V) versus specific capacity (mAh/g)showing charge/discharge characteristics of an embodiment ofall-solid-state secondary battery; and

FIG. 10 is a graph of discharge specific capacity (mAh/g) versus currentdensity (mA/cm²) showing output characteristics when using an anodeactive material comprising Ketjen black and platinum (Pt).

DETAILED DESCRIPTION

Various example embodiments will now be described more fully withreference to the accompanying drawings in which example embodiments areshown.

It will be understood that when an element is referred to as being “on,”“connected,” or “coupled” to another element, it can be directly on,connected, or coupled to the other element, or intervening elements maybe present. In contrast, when an element is referred to as being“directly on,” “directly connected,” or “directly coupled” to anotherelement, there are no intervening elements present. As used herein theterm “and/or” includes any and all combinations of one or more of theassociated listed items. “Or” means “and/or.” Expressions such as “atleast one of,” when preceding a list of elements, modify the entire listof elements and do not modify the individual elements of the list.

It will be understood that, although the terms “first,” “second” etc.may be used herein to describe various elements, components, regions,layers, and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areused to distinguish one element, component, region, layer, or sectionfrom another element, component, region, layer, or section. Thus, afirst element, component, region, layer, or section discussed belowcould be termed a second element, component, region, layer, or sectionwithout departing from the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” “rear,” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”other elements or features would then be oriented “above” the otherelements or features. Thus, the exemplary term “below” can encompassboth an orientation of above and below. The device may be otherwiseoriented (rotated 90 degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly. In thedrawings, some of the elements may be omitted, but such omissions arenot intended to exclude the omitted elements, but are intended to helpunderstanding of the features of the present inventive concept.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of example embodiments.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “includes”and/or “including,” “haves” and/or “having,” and “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” may mean within one or morestandard deviations, or within ±30%, 20%, 10%, or ±5% of the statedvalue.

All ranges disclosed herein are inclusive of the endpoints, unlessclearly indicated otherwise, and the endpoints are independentlycombinable with each other (e.g., ranges of “up to 25 wt %, or, morespecifically, 5 wt % to 20 wt %”, is inclusive of the endpoints and allintermediate values of the ranges of “5 wt % to 25 wt %,” such as “10 wt% to 25 wt %” and “5 wt % to 15 wt %”, etc.). Reference throughout thespecification to “some embodiments”, “an embodiment”, “anotherembodiment”, and so forth, means that a particular element described inconnection with the embodiment is included in at least one embodimentdescribed herein, and may or may not be present in other embodiments. Inaddition, it is to be understood that the described elements may becombined in any suitable manner in the various embodiments. A“combination thereof” is open and includes any combination comprising atleast one of the listed components or properties optionally togetherwith a like or equivalent component or property not listed.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofexample embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, such as those defined incommonly-used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of the relevant artand will not be interpreted in an idealized or overly formal senseunless expressly so defined in the present specification.

Hereinafter, an all-solid-state secondary battery, methods ofmanufacture thereof, and methods of charging the same will be describedin further detail with reference to the accompanying drawings. Widthsand thicknesses of layers or regions illustrated in the accompanyingdrawings may be exaggerated for clarity and convenience of explanation.Throughout the detailed description, like reference numerals denote likeelements.

Also provided is a method of using at least one of lithium or a lithiumalloy as an anode active material.

Also disclosed is a method of using an anode active material, which doesnot comprise lithium, on an anode current collector, in which lithium isdeposited between the anode current collector and the anode activematerial layer during charge, wherein the anode current collectorcomprises a metal that is not alloyable with lithium and does not form acompound with lithium.

Structure of All-Solid-State Secondary Battery

First, a structure of an all-solid-state secondary battery 100 accordingto a first embodiment will be described with reference to FIG. 1 . Asillustrated in FIG. 1 , the all-solid-state secondary battery 100 mayinclude a cathode 10, an anode 20, and a solid electrolyte layer 30between the cathode and the anode.

Cathode

The cathode 110 comprises a cathode active material layer 112. Thecathode 110 may optionally comprise a cathode current collector 111 onthe cathode active material layer 112. The cathode current collector 111may be a form of a plate or a foil and may comprise, for example, atleast one of indium (In), copper (Cu), magnesium (Mg), stainless steel,titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum(Al), germanium (Ge), or lithium (Li), or an alloy thereof. In anembodiment in which the cathode current collector 111 is omitted, thecathode active material layer 112 may perform the function of currentcollection.

The cathode active material layer 112 may include a cathode activematerial and a solid electrolyte. In addition, the solid electrolyteincluded in the cathode 110 may be similar to or different from a solidelectrolyte included in the solid electrolyte layer 130.

In an embodiment, the cathode active material comprises a first solidelectrolyte, and the solid electrolyte layer comprises a second solidelectrolyte, wherein the first solid electrolyte and the second solidelectrolyte may be independently selected. A detailed description of thesolid electrolyte will be provided below in the description of the solidelectrolyte layer 130.

In an embodiment, the solid electrolyte may be included in the cathodelayer 112 in an amount of about 1 wt % to about 50 wt %, based on thetotal weight of the cathode layer 112.

The cathode active material may be any suitable cathode active materialcapable of reversibly intercalating, e.g., incorporating anddeintercalating, e.g., deincorporating of lithium ions.

For example, the cathode active material may comprise at least one of alithium metal oxide, a lithium metal phosphate, a sulfide, or an oxide.The lithium metal oxide may comprise a lithium transition metal oxide,and may comprise, for example, at least one of lithium cobalt oxide(hereinafter, referred to as “LCO”), lithium nickel oxide, lithiumnickel cobalt oxide, lithium nickel cobalt aluminum oxide (hereinafter,referred to as “NCA”), lithium nickel cobalt manganese oxide(hereinafter, referred to as “NCM”), or lithium manganate. An example ofa lithium phosphate is lithium iron phosphate. The sulfides may compriseat least one of nickel sulfide, copper sulfide, and lithium sulfide. Theoxide may comprise at least one of iron oxide or vanadium oxide, or thelike. The cathode active materials may be used alone, or a combinationof cathode active materials may be used.

In an embodiment, the cathode active material may include a lithiumtransition metal oxide having a layered halite structure. As usedherein, the term “layered halite structure” refers to a structure inwhich oxygen atomic layers and metal atomic layers are alternatelyarranged regularly in a <111> direction of a cubic halite structure, andas a result, each atomic layer forms a two-dimensional plane. The term“cubic halite structure” as used herein refers to a sodium chloridestructure, which is a type of crystal structure, and, in particular, astructure in which face-centered cubic lattices formed by cations andanions, respectively, are dislocated with respect to each other by ½ ofa unit cell dimension.

The lithium transition metal oxide having a layered halite structure maybe, for example, at least one of a lithium transition metal oxiderepresented by the formula LiNi_(x)Co_(y)Al_(z)O₂ (NCA) wherein 0<x<1,0<y<1, and 0<z<1, wherein x+y+z=1, or the formula LiNi_(x)Co_(y)Mn_(z)O₂(NCM) wherein 0<x<1, 0<y<1, and 0<z<1, wherein x+y+z=1. Thestoichiometric coefficients x, y, and z may be independently selectedfor each lithium transition metal oxide.

When the cathode active material includes the lithium transition metaloxide having a layered halite structure, energy density and thermalstability of the all-solid-state secondary battery 100 may be enhanced.

The cathode active material may be covered by a coating. In this regard,the coating may comprise any suitable coating for a cathode activematerial of an all-solid-state secondary battery. The coating layer mayinclude, for example, LiNbO₃, Li₄TiO₅O₁₂, Li₂O—ZrO₂, a lithium lanthanumzirconate such as Li_(7−3x)Al_(x)La₃Zr₂O₁₂ wherein 0≤x≤1, e.g.,Li₇La₃Zr₂O₁₂, or the like. Additional details of the coating can bedetermined by one of skill in the art without undue experimentation, andthus are not further elaborated upon here for clarity.

In addition, the cathode active material comprises a lithium transitionmetal oxide such as NCA, NCM, or the like, and when Ni is included inthe cathode active material, capacity of the all-solid-state secondarybattery 100 may be increased, resulting in reduced metal deposition onthe cathode active material when the battery is in a charged state.Accordingly, the all-solid-state secondary battery 100 according to thepresent embodiment may have enhanced long-term reliability in a chargedstate and improved cycle characteristics.

In an embodiment, the cathode active material may be in the form of aparticle. The particle may have any suitable shape, may have arectilinear or curvilinear shape, and may be spherical, oval, or acombination thereof. In addition, the particle diameter of the cathodeactive material is not particularly limited, and may have any suitableparticle diameter for a cathode active material of an all-solid-statesecondary batteries. The particle diameter may be about 500 nanometers(nm) to about 20 micrometers (μm), about 1 μm to about 15 μm, or about 5μm to about 10 μm. Unless specified otherwise, particle diameter is aD50 particle diameter and determined by laser light scattering. Theamount of the cathode active material of the cathode 110 is notparticularly limited, and any suitable amount for a cathode of anall-solid-state secondary battery may be used. The content of thecathode active material in the cathode may be about 50 weight percent(wt %) to about 99 wt %, about 60 wt % to about 95 wt %, or about 70 wt% to about 90 wt %, based on a total weight of the cathode. Also, thecathode active material may be contained in the cathode active materiallayer 12 in an amount of about 55 wt % to about 99 wt %, about 65 wt %to about 97 wt %, or about 75 wt % to about 95 wt %, based on a totalweight of the cathode active material layer 112.

In addition, the cathode 110 may comprise, for example, an appropriateamount of an additive, such as a conductive agent, a binder, a filler, adispersant, or the like, in addition to the cathode active material andthe solid electrolyte.

The conductive agent may be, for example, graphite, carbon black,acetylene black, Ketjen black, carbon fiber, metallic powder, or thelike. A combination of conductive agents may be used. Also, theconductive agent may be included in any suitable amount, e.g., about 0.5wt % to about 10 wt %, based on a total weight of the cathode. Theconductive agent may be included in an amount of about 0.5 wt % to about10 wt %, based on a total weight of the cathode active material layer112.

If desired, the cathode 110 may comprise a binder. The binder maycomprise, for example, styrene butadiene-rubber (SBR),polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or thelike. A combination of binders may be used. Also, the binder may beincluded in any suitable amount, e.g., about 0.1 wt % to about 10 wt %,based on a total weight of the cathode. The binder may be included in anamount of about 0.1 wt % to about 10 wt %, based on a total weight ofthe cathode active material layer 112.

Anode

The anode 120 may include an anode current collector 121 and an anodeactive material on the current collector. In an embodiment, the anodecomprises an anode current collector 121 and an anode active materiallayer 122 on the anode current collector 121.

The anode current collector 121 may comprise a material that is notreactive with lithium, i.e., does not form either an alloy or a compoundwith lithium. A suitable material for the anode current collector 121may be, for example, Cu, stainless steel, Ti, Fe, Co, or Ni. Acombination comprising at least one of the foregoing may be used. Theanode current collector 121 may comprise a single type of metal, analloy of two or more metals, and may optionally comprise a coating onthe metal. The shape of the anode current collector is not specificlimited, the anode current collector may be rectilinear or curvilinear,and the anode current collector 121 may be, for example, in the form ofa plate or foil. In an embodiment, the anode current collector 121 maybe in the form of a clad foil.

In an embodiment, as illustrated in FIG. 3 , a plating layer 124 may beformed on a surface of the anode current collector 121. The platinglayer 124 may be in the form of a thin film and may include an element(e.g., a metal) that is alloyable with lithium. As used herein,“alloyable with lithium” means that a material (e.g., element or metal)is capable of forming an alloy with lithium.

Examples of the element that is alloyable with lithium include gold(Au), silver (Ag), zinc (Zn), tin (Sn), indium (In), silicon (Si),aluminum (Al), and bismuth (Bi). The plating layer 124 may comprise atleast one of the foregoing alloyable elements, or an alloy thereof.While not wanting to be bound by theory, it is understood that due tothe presence of the plating layer 124, a deposition form of the metallayer 223 as shown in FIG. 4 may have reduced roughness, and may besmoother and/or flattened, and the all-solid-state secondary battery 200may have enhanced characteristics.

Turning now to FIG. 3 , in an embodiment, the thickness of the platinglayer 124 is not particularly limited, and the thickness may range fromabout 1 nanometer (nm) to about 500 nm, about 2 nm to about 400 nm, orabout 4 nm to about 300 nm. When the thickness of the plating layer 124is less than 1 nm, the function of the plating layer 124 may not besufficiently exhibited. Without being bound by theory, when thethickness of the plating layer 124 is greater than about 500 nm, theplating layer 124 itself may intercalate lithium, and thus a depositionamount of lithium at an anode is decreased, and, accordingly, thecharacteristics of the all-solid-state secondary battery 100 maydeteriorate. The plating layer 124 may be formed on the anode currentcollector 121 by, for example, vacuum deposition, sputtering, plating,or the like.

The anode active material layer 122 comprises an anode active materialthat is alloyable with lithium, intercalates lithium, or forms acompound with lithium. The anode active material may comprise at leastone of amorphous carbon, a metal, or a semiconductor. In other words,when used as the anode active material, at least one of the amorphouscarbon, metal, and semiconductor are selected from materials that arealloyable with lithium, intercalate lithium, or form a compound withlithium. In this regard, the metal or the semiconductor may be, forexample, gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver(Ag), aluminum (Al), bismuth (Bi), tin (Sn), and zinc (Zn), or acombination thereof. The amorphous carbon may be, for example, carbonblack (CB), acetylene black (AB), furnace black (FB), Ketjen black (KB),graphene, or a combination thereof, or the like. An anode activematerial may comprise, for example, at least one of amorphous carbon,Au, Pt, Pd, Si, Ag, Al, Bi, Sn, or Zn. For example, amorphous carbon orat least one of Au, Pt, Pd, Si, Ag, Al, Bi, Sn, or Zn may be used. Inanother embodiment, the anode active material layer 22 may compriseamorphous carbon and at least one of Au, Pt, Pd, Si, Ag, Al, Bi, Sn, orZn. For example, the anode active material layer 22 may include a Siparticle that is coated with amorphous carbon, preferably wherein thecoating has a thickness of about 1 nm to about 10 nm. In an embodimentthe element that is alloyable with lithium may be omitted and onlyamorphous carbon used. A weight ratio of the amorphous carbon to theelement that is alloyable with lithium may be about 10:1 to about 1:10,about 5:1 to about 1:5, or about 3:1 to about 1:3. In an embodiment, thecontent of the amorphous carbon may be about 10 wt % to about 99 wt %,about 20 wt % to about 95 wt %, or about 30 wt % to about 99 wt %, basedon a total weight of the anode. In an embodiment, the amorphous carbonmay be present in an amount of about 20 wt % to about 99 wt %, about 40wt % to about 98 wt %, or about 60 wt % to about 95 wt %, based on atotal weight of the anode active material layer. In an embodiment, thecontent of the element that is alloyable with lithium may be about 10 wt% to about 99 wt %, about 20 wt % to about 95 wt %, or about 30 wt % toabout 99 wt %, based on a total weight of the anode. In an embodiment,the element that is alloyable with lithium may be present in an amountof about 20 wt % to about 99 wt %, about 40 wt % to about 98 wt %, orabout 60 wt % to about 95 wt %, based on a total weight of the anodeactive material layer. When the anode active material includes thesematerials, the characteristics of the all-solid-state secondary battery100 may be further enhanced.

An average particle size D50 (e.g., average particle diameter) of theanode active material may be about 4 micrometers (μm) or less, about 10nm to about 1 μm, or about 10 nm to about 100 nm. As noted above, theaverage particle size D50 (e.g., average particle diameter) of the anodeactive material may be a median diameter D50 as measured by a laserlight scattering. A lower limit of the particle diameter may be about 10nm, but anode active material is not particularly limited thereto.

A ratio of charge capacity of the anode active material layer 122 to acharge capacity of the cathode active material layer 112, i.e., acapacity ratio, may satisfy Equation 1:

0.01≤(b/a)<0.5  Equation 1

-   -   wherein a is the initial charge capacity of the cathode active        material layer 112, determined from a first open circuit voltage        to a maximum charging voltage vs. Li/Li⁺, and wherein b is the        initial charge capacity of the anode active material layer 122,        determined from a second open circuit voltage to 0.01 Volts (V)        vs. Li/Li⁺. The charge capacities, a and b, are determined        separately by using all-solid-state half-cells with Li counter        electrodes from the first open circuit voltage to a maximum        charging voltage (vs. Li/Li⁺) for the cathode, and the second        open circuit voltage to 0.01 V (vs. Li/Li⁺) for the anode,        respectively.

The maximum charging voltage of the cathode depends on the cathodeactive material. In an embodiment, the maximum charge voltage of thecathode active material is determined as the maximum voltage where acell comprising the cathode active material satisfies the safetyconditions described in Appendix A of “Safety Requirements For PortableSealed Secondary Cells, And For Batteries Made From Them, For Use InPortable Applications”, Japanese Standards Association, JISC8712:2015,the entire content of which is incorporated by reference herein.According to an embodiment, the maximum charging voltage can be about 3volts (V) to about 5 V, about 3.5 V to about 4.5 V, or about 4.2 voltsto about 5 volts, or about 4 V to about 4.4 V, or about 4.1 V to about4.3 V, or about 4.2 V, or about 4.25 V. In an embodiment, e.g., when thecathode active material is lithium cobalt oxide (LCO), NCA, or NCM, themaximum charging voltage is 4.1 V or 4.2 V vs. Li/Li⁺. In an embodiment,e.g., when the cathode active material is lithium cobalt oxide (LCO),NCA, or NCM, the maximum charging voltage is about 4.25 V vs. Li/Li⁺.

In another embodiment, the ratio of the charge capacity of the anodeactive material layer to the initial charge capacity of the cathodeactive material layer satisfies a condition of Equation 1A:

0.01<(b/a)<0.25.  Equation 1A

In yet another embodiment, the ratio of the initial charge capacity ofthe anode active material layer to the initial charge capacity of thecathode active material layer satisfies a condition of Equation 1B:

0.01<(b/a)<0.2.  Equation 1B

In still another embodiment, the ratio of the initial charge capacity ofthe anode active material layer to the initial charge capacity of thecathode active material layer satisfies a condition of Equation 1C:

0.01<(b/a)<0.1.  Equation 1C

In this regard, the charge capacity of the cathode active material layer112 can be obtained by multiplying the charge specific capacity of thecathode active material by the mass of cathode active material in thecathode active material layer 112 as shown in Equation 2.

Q=q·m  Equation 2

-   -   wherein Q is the initial charge capacity (mAh), q is the        specific capacity of the active material (mAh/g), and m is the        mass of the active material (g).

When multiple cathode active materials are used, the initial chargecapacity is determined based on the relative content of each cathodeactive material, e.g., by multiplying the charge specific capacity bythe mass of each cathode active material, and a sum of these values isused as the initial charge capacity of the cathode active material layer112. The initial charge capacity of the anode active material layer 122is also calculated in the same manner. That is, the initial chargecapacity of the anode active material layer 122 is obtained bymultiplying charge specific capacity of the anode active material by themass of anode active material in the anode active material layer 122.When multiple anode active materials are used, a value of the chargespecific capacity multiplied by the mass for each anode active materialis calculated, and a sum of these values is used as the initial chargecapacity of the anode active material layer 122.

The charge specific capacity of each of the cathode and anode activematerials may be determined using an all-solid-state half-cell usinglithium metal as a counter electrode. The initial charge capacity ofeach of the cathode active material layer and the anode active materiallayer can be directly measured using separate all-solid-state half-cellsat a current density of, for example, 0.1 milliamperes per squarecentimeter (mA/cm²). For a cathode, the measurement can be made with anoperating voltage (vs. Li/Li⁺) from a first open circuit voltage (OCV)to the maximum charging voltage, for example 4.25 Volts (V). For theanode, the measurement can be made with an operating voltage (vs. Li/L⁺)from a second OCV to 0.01 V for the anode. For example, the all-solidstate half-cell with the cathode active material layer can be charged ata constant current density of 0.1 mA/cm² from a first OCV to 4.25 V, andthe all-solid state half-cell with the anode active material layer canbe discharged with a constant current density of 0.1 mA/cm² from a firstOCV to 0.01 V. In another embodiment, the all-solid-state half-cell withthe cathode active material layer can be charged at a constant currentdensity of 0.5 mA/cm² from a first OCV to 4.25 V, charged at a constantvoltage of 4.25 V until the current density reached 0.2 mA/cm², anddischarged at a constant current density of 0.5 mA/cm² until the voltagereached 2.0 V. For example, the cathode may be charged from a first OCVto about 3 V, or from a first OCV to about 4 V, or from a first OCV toabout 4.1 V, or from a first OCV to about 4.2 V, or from a first OCV toabout 5 V. The maximum charging voltage, or discharging bias, for thecathode is not limited thereto. The maximum operating voltage of thecathode active material can be determined as the maximum voltage wherethe cell satisfies the safety conditions according to the description inthe Appendix A of “Safety Requirements For Portable Sealed SecondaryCells, And For Batteries Made From Them, For Use In PortableApplications”, Japanese Standards Association, JISC8712:2015.

The all-solid-state half-cell can be prepared by pressing a solid stateelectrolyte material (e.g., 200 mg of L₆PS₅Cl) at a pressure of 40megapascals (MPa) to provide a pellet having a diameter of 1.3 cm and athickness of 1 mm. The solid state electrolyte pellet is then disposedbetween electrode disks each having a diameter of 1.3 cm that are madefrom the respective cathode and anode active materials. The assembledlayers are then sandwiched between two stainless steel disks, which areused as current collectors, and then subsequently disposed into apoly(tetrafluoroethylene) cylinder. This assembly is pressed at apressure of about 300 MPa for 1 minute and then placed in a stainlesssteel outer casing. The assembled half-cell was then pressed at apressure of about 22 MPa to maintain electrochemical contact duringcharge capacity measurements.

The charge specific capacity is calculated by dividing the initialcharge capacity by the mass of each active material. The charge capacityof each of the cathode active material layer 112 and the anode activematerial layer 122 is an initial charge capacity measured during the1^(st) charge.

In an embodiment, the initial charge capacity of the cathode activematerial layer 112 exceeds the initial charge capacity of the anodeactive material layer 122. In an embodiment, when the all-solid-statesecondary battery 100 is charged, the initial charge capacity of theanode active material layer 122 is exceeded. That is, the anode activematerial layer 122 is overcharged. As used herein, the term“overcharged” refers to a voltage greater than the open circuit voltageof the “fully-charged” battery or half-cell, and is further defined inAppendix A of “Safety Requirements For Portable Sealed Secondary Cells,And For Batteries Made From Them, For Use In Portable Applications”,Japanese Standards Association, JISC8712:2015, the entire content ofwhich is incorporated by reference herein. At the initial stage ofcharging, lithium is incorporated into the anode active material layer122. As used herein, “incorporated” means the anode active materiallayer is capable of intercalating or alloying a lithium ion, or can forma compound with lithium (e.g., CoO+2Li⁺→Li₂O+Co). That is, the anodeactive material may form an alloy or compound with a lithium iontransferred from the cathode 110. When charging is performed such thatthe initial charge capacity of the anode active material layer 122 isexceeded, as illustrated in FIG. 2 , lithium is deposited on a surface,e.g., rear surface of the anode active material layer 122, i.e., betweenthe anode current collector 121 and the anode active material layer 122,and the metal layer 123 is formed as a layer of lithium. The metal layer123 may be primarily lithium (e.g., lithium metal). In an embodiment,the metal layer (i.e. lithium layer) can be deposited anywhere betweenthe anode current collector and the solid electrolyte layer, for examplewithin the anode active material layer, between the anode activematerial layer and the anode current collector, between the platinglayer and the anode current collector, between the plating layer and theanode active material layer, or a combination thereof. Without beingbound by theory, this may occur due to the use of a particular material,e.g., a material alloyable with lithium or a material capable of forminga compound with lithium, as an anode active material. During discharge,lithium of the anode active material layer 122 and the metal layer 123is ionized and transferred to the cathode 110. Thus, in theall-solid-state secondary battery 100, lithium may be used as an anodeactive material. In addition, since the anode active material layer 122covers the metal layer 123, the anode active material layer 122 may actas a protective layer for the metal layer 123, and also may inhibit thedeposition and growth of dendrites. This may inhibit the short circuitand capacity reduction of the all-solid-state secondary battery 100, andfurthermore, may enhance the characteristics of the all-solid-statesecondary battery 100.

In an embodiment, the capacity ratio (i.e., b/a) is greater than 0.01.When the capacity ratio is 0.01 or less, the characteristics of theall-solid-state secondary battery 100 may deteriorate. While not wantingto be bound by theory, this is understood to be because the anode activematerial layer 122 may not sufficiently function as a protective layer.For example, when the thickness of the anode active material layer 122is too small, the capacity ratio may be 0.01 or less. In this case, whencharging and discharging are repeated, the anode active material layer122 may collapse and a dendrite may be deposited and grow. As a result,the characteristics of the all-solid-state secondary battery 100 maydeteriorate.

In another embodiment, the anode active material may further include amixture of a first particle comprising an amorphous carbon and a secondparticle comprising a metal, a semiconductor, or a combination thereof.The metal or the semiconductor may include, for example, Au, Pt, Pd, Si,Ag, Al, Bi, Sn, Zn, a combination thereof, or the like. In this regard,the amount of the second particles may range from about 8 wt % to about60 wt %, or about 10 wt % to about 50 wt %, with respect to a totalweight of the mixture. In this case, the characteristics of theall-solid-state secondary battery 100 may be further enhanced. As usedherein, the terms “mass” and “weight” are equivalent.

In an embodiment, the anode active material layer 122 may furtherinclude a binder. Examples of the binder may include, but are notlimited to, styrene butadiene rubber (SBR), polytetrafluoroethylene,polyvinylidene fluoride, and polyethylene. One of these binders may beused, or two or more of these binders may be used.

When the anode active material layer 122 further includes a binder, theanode active material layer 122 may be stabilized on the anode currentcollector 121. For example, when the binder is not included in the anodeactive material layer 122, the anode active material layer 122 may bemore easily detached from the anode current collector 121. A portion ofthe anode current collector 21, from which the anode active materiallayer 122 may be detached, is exposed, and thus a short circuit mayoccur. The anode active material layer 122 may be formed by, forexample, by coating a slurry, in which materials constituting the anodeactive material layer 122 are dispersed, onto the anode currentcollector 121 and drying the coated anode current collector 121, whichwill be described below in further detail. By including a binder in theanode active material layer 122, the anode active material may be stablydispersed in the slurry. As a result, when the slurry is coated onto theanode current collector 121 by, for example, screen printing, cloggingof a screen (e.g., clogging due to an aggregate of the anode activematerial) may be suppressed.

In an embodiment, when the binder is included in the anode activematerial layer 122, the amount of the binder may range from about 0.3 wt% to about 15 wt %, based on a total weight of the anode activematerial. When the amount of the binder is less than 0.3 wt %, based ona total weight of the anode active material, the strength of the activematerial layer, or an adhesion of the anode active material layer to theanode current collector, may be insufficient, and characteristics of theanode active material layer may deteriorate and it may be difficult totreat or handle the anode active material layer. When the amount of thebinder is greater than 20 wt %, based on a total weight of the anodeactive material, the characteristics of the all-solid-state secondarybattery 100 may deteriorate. In some embodiments, a lower limit of theamount of the binder may be about 3 wt %, based on a total weight of theanode active material. For example, the binder may be included in theanode active material layer 22 in an amount of about 3 wt % to about 15wt %, based on a total weight of the anode active material.

The thickness of the anode active material layer 122 is not particularlylimited as long as the anode active material layer satisfies thecondition of Equation 1 above, and may range from about 1 μm to about 20μm. When the thickness of the anode active material layer 22 is lessthan 1 μm, the characteristics of the all-solid-state secondary battery1 may not be sufficiently enhanced. When the thickness of the anodeactive material layer 122 is greater than 20 μm, the anode activematerial layer 122 has a high resistance value, resulting ininsufficient enhancement of the characteristics of the all-solid-statesecondary battery 100. When the above-described binder is used, thethickness of the anode active material layer 122 may be adjusted to anappropriate level.

In an embodiment, the all-solid-state secondary battery may furtherinclude an additive in the anode active material layer 122. The additivemay comprise a filler, a dispersant, or an ion conductive agent, or thelike.

Solid Electrolyte Layer

The solid electrolyte layer 130 includes a solid electrolyte disposedbetween the cathode 110 and the anode 120.

The solid electrolyte may include, for example, a sulfide-based solidelectrolyte material. The sulfide-based solid electrolyte materialcomprise, for example, Li₂S—P₂S₅, Li₂S—P₂S₅—LiX where X is a halogenelement, e.g., iodine (I) or chlorine (Cl), Li₂S—P₂S₅—Li₂O,Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr,Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI, Li₂S—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃,Li₂S—P₂S₅—Z_(m)S_(n) where m and n are positive numbers, and Z is one ofgermanium (Ge), zinc (Zn), and gallium (Ga), Li₂S—GeS₂,Li₂S—SiS₂—Li₃PO₄, Li₂S—SiS₂-Li_(p)MO_(q) where p and q are positivenumbers, and M is one of phosphorus (P), silicon (Si), germanium (Ge),boron (B), aluminum (Al), gallium (Ga), and indium (In), or the like. Inthis regard, the sulfide-based solid electrolyte material is prepared bytreating a starting material (e.g., Li₂S, P₂S₅, or the like) by a metalquenching method, a mechanical milling method, or the like. In addition,heat treatment may be performed after the treatment. The solidelectrolyte may be amorphous, crystalline, or in a mixed form.

In an embodiment, the sulfide-based solid electrolyte material mayinclude at least sulfur (S), phosphorus (P), and lithium (Li) asconstitutional elements, and in a particular embodiment a materialincluding Li₂S—P₂S₅ may be used. However, these examples are providedfor illustrative purposes only, and suitable materials may vary.

In an embodiment, when the material including Li₂S—P₂S₅ is used as asulfide solid electrolyte material for forming the solid electrolyte, amixing molar ratio of Li₂S to P₂S₅ may be range from, for example, about50:50 to about 90:10. In addition, the solid electrolyte layer 130 mayfurther include a binder. The binder included in the solid electrolytelayer 130 may be, for example, SBR, polytetrafluoroethylene,polyvinylidene fluoride, polyethylene, polyacrylic acid, or the like.The binder of the solid electrolyte layer 30 may be identical to ordifferent from the binders of the cathode active material layer 112 andthe anode active material layer 122.

Method of Manufacturing All-Solid-State Secondary Battery

Hereinafter, a method of manufacturing the all-solid-state secondarybattery 100 according to an embodiment will be described. Theall-solid-state secondary battery 100 according to the presentembodiment may be manufactured by fabricating the cathode 110, the anode120, and the solid electrolyte layer 130, and then stacking theselayers.

Cathode Formation

First, materials (e.g., a cathode active material, a binder, and thelike) for forming the cathode active material layer 112 are added to anon-polar solvent to prepare a slurry (the slurry may be a paste, it isalso applied to other slurries). Subsequently, the prepared slurry iscoated onto the cathode current collector 111 and dried. Thereafter, theobtained stacked structure is pressed (e.g., pressing using hydrostaticor hydraulic pressure), thereby completing the formation of the cathode110. The pressing process may be omitted in some embodiments. A mixtureof materials for forming the cathode active material layer 112 may besubjected to compaction molding into a pellet form or elongated(molding) into a sheet form, thereby completing the formation of thecathode 110. When the cathode 110 is formed using this method, thecathode current collector 111 may be omitted.

Anode Formation

First, materials (e.g., an anode active material, a binder, and thelike) for forming the anode active material layer 122 are added to apolar solvent or a non-polar solvent to prepare a slurry. Subsequently,the prepared slurry is coated onto the anode current collector 121 anddried. Thereafter, the obtained stacked structure is pressed (e.g.,pressing using hydrostatic or hydraulic pressure), thereby completingthe formation of the anode 20. The pressing process is optional and maybe omitted.

Formation of Solid Electrolyte Layer

The solid electrolyte layer 30 may be formed using a solid electrolyteformed of a sulfide-based solid electrolyte material.

First, a solid electrolyte starting material is treated by meltquenching or mechanical milling.

For example, when the melt quenching is used, starting materials (e.g.,Li₂S, P₂S₅, and the like) may be mixed in certain amounts to prepare apellet form, and the prepared pellet form may be allowed to react in avacuum state at a predetermined reaction temperature, followed byquenching, thereby completing the preparation of the sulfide solidelectrolyte material. In an embodiment, the reaction temperature of themixture of Li₂S and P₂S₅ ranges from, for example, about 400° C. toabout 1,000° C., or about 800° C. to about 900° C. In anotherembodiment, reaction time may range from, for example, about 0.1 hoursto about 12 hours, or about 1 hour to about 12 hours. In still anotherembodiment, a quenching temperature of the reaction product is 10° C. orless, or 0° C. or less, and a quenching rate of the reaction productranges from about 1° C./sec to about 10,000° C./sec, or about 1° C./secto about 1,000° C./sec.

In an embodiment, when mechanical milling is used, solid electrolytestarting materials (e.g., Li₂S, P₂S₅, and the like) may be allowed toreact while stirred using a ball mill or the like, thereby preparing asulfide-based solid electrolyte material. In another embodiment, astirring rate and stirring time of the mechanical milling method are notparticularly limited, but the faster the stirring rate, the faster theproduction rate of the sulfide-based solid electrolyte material, and thelonger the stirring time, the higher the conversion rate of rawmaterials into the sulfide-based solid electrolyte material.

Thereafter, the mixed starting materials obtained by melt quenching ormechanical milling may be heat-treated at a predetermined temperatureand then pulverized, thereby preparing a solid electrolyte having aparticle form. When the solid electrolyte has glass transitionproperties, the solid electrolyte may be converted to a crystalline formfrom an amorphous form by heat treatment.

Subsequently, the solid electrolyte obtained using the method may bedeposited using a known film formation method, for example, by aerosoldeposition, cold spraying, sputtering, or the like, thereby preparingthe solid electrolyte layer 30. In still another embodiment, the solidelectrolyte layer 30 may be formed by pressing solid electrolyteparticles. In yet another embodiment, the solid electrolyte layer 30 maybe formed by mixing the solid electrolyte with a solvent and a binder,followed by coating, drying, and pressing, thereby completing theformation of the solid electrolyte layer 30.

Manufacture of all-Solid-State Secondary Battery

The cathode 110, the anode 120, and the solid electrolyte layer 130,which are formed using the above-described methods, are stacked suchthat the solid electrolyte layer 130 is arranged between the cathode 110and the anode 120, followed by pressing (e.g., pressing usinghydrostatic or hydraulic pressure), thereby completing the manufactureof the all-solid-state secondary battery 100.

For example, the all-solid-state secondary battery 100 may be pressedduring the manufacturing operation. The pressing may be applied bysandwiching the assembled battery between two hard plates made fromstainless steel, brass, aluminum, glass, or the like, and tighteningwith screws to apply pressure. The applied pressure may be about 0.5 MPato about 10 MPa.

Method of Charging All-Solid-State Secondary Battery

A method of charging the all-solid-state secondary battery 100 will nowbe described. In an embodiment, the all-solid-state secondary battery100 is charged such that the initial charge capacity of the anode activematerial layer 122 is exceeded. That is, the anode active material layer122 is overcharged. At the initial stage of charging, lithium isincorporated into the anode active material layer 122. Without beingbound by theory, the anode active material layer can be overcharged whenlithium electrochemically reacts on the interface between the anodeactive material layer and the solid electrolyte layer. The reactedlithium may diffuse within the anode active material particles, and whenovercharged, the lithium atoms may precipitate at or near the currentcollector. When charging is performed such that the initial chargecapacity of the anode active material layer 122 is exceeded, asillustrated in FIG. 2 , lithium is deposited on a rear surface of theanode active material layer 122, i.e., between the anode currentcollector 121 and the anode active material layer 122, and the metallayer 123 is formed by such lithium deposition. During discharge,lithium of the anode active material layer 122 and the metal layer 123are ionized and transferred to the cathode 110. In this regard, theanode active material layer is capable of incorporating, e.g.,intercalating or alloying, and capable of deincorporating, e.g.,deintercalating or dealloying, a lithium ion. Thus, in the all-solidsecondary battery 100, lithium may be used as an anode active material.In addition, since the anode active material layer 122 covers the metallayer 123, the anode active material layer 122 may act as a protectivelayer for the metal layer 123, and also inhibit the deposition andgrowth of dendrites. This inhibits the short circuit and capacityreduction of the all-solid-state secondary battery 100, and furthermore,may enhance characteristics of the all-solid-state secondary battery100. In addition, in the first embodiment, since the metal layer 123 isnot previously formed, manufacturing costs of the all-solid secondarybattery 100 may be reduced. In this case, the anode current collector121, the anode active material layer 122, and a region (interface)therebetween may be Li-free regions at an initial state of or afterdischarging of the all-solid-state secondary battery 100.

Structure of All-Solid-State Secondary Battery of FIG. 4

Next, a structure of an all-solid-state secondary battery 200 accordingto another embodiment will be described with reference to FIG. 4 . Asillustrated in FIG. 4 , the all-solid-state secondary battery 200includes the cathode 210, the anode 220, and the solid electrolyte layer230. Configurations of the cathode 210 and the solid electrolyte layer230 are the same as those described for FIG. 1 .

Anode

The anode 220 includes the anode current collector 221, the anode activematerial layer 222, and the metal layer 223. That is, according to anembodiment the metal layer 223 is formed between the anode currentcollector 221 and the anode active material layer 222 by overcharging ofthe anode active material layer 222. According to another embodiment,the metal layer 223 is previously (i.e., prior to initial charging)formed between the anode current collector 221 and the anode activematerial layer 222.

Configurations of the anode current collector 221 and the anode activematerial layer 222 are the same as those described above. The metallayer 223 may include lithium or a lithium alloy. That is, the metallayer 223 may function as a lithium reservoir. The lithium alloy may be,for example, a Li—Al alloy, a Li—Sn alloy, a Li—In alloy, a Li—Ag alloy,a Li—Au alloy, a Li—Zn alloy, a Li—Ge alloy, a Li—Si alloy, or the like.The metal layer 223 may be formed of one of these alloys or lithium, oran alloy thereof. In an embodiment shown in FIG. 4 , since the metallayer 223 acts as a lithium reservoir, the all-solid-state secondarybattery 1 a may have further enhanced characteristics.

In an embodiment, the thickness of the metal layer 223 may range fromabout 1 μm to about 200 μm, but is not particularly limited. When thethickness of the metal layer 223 is less than 1 μm, the function of themetal layer 223 as a reservoir may not be sufficiently exhibited. Whenthe thickness of the metal layer 223 is greater than 200 μm, the massand volume of the all-solid-state secondary battery 1 a may beincreased, resulting in rather deteriorated characteristics. The metallayer 223 may be, for example, metal foil having a thickness within theabove-described range.

Method of Manufacturing All-Solid-State Secondary Battery

Hereinafter, a method of manufacturing the all-solid-state secondarybattery 200 according to the second embodiment will be described. Thecathode 210 and the solid electrolyte layer 230 are formed in the samemanner as in the first embodiment.

Anode Formation

In an embodiment depicted in FIG. 4 , the anode active material layer222 is arranged on the metal layer 223. In an embodiment, the metallayer 223 may include a metal foil. Since it is difficult to form theanode active material layer 222 on Li foil or Li alloy foil, the anode220 may be formed using the following method.

First, the anode active material layer 222 is formed on a certain basematerial (e.g., a Ni plate) using the same method as that describedabove. In particular, materials for forming the anode active materiallayer 222 are added to a solvent to prepare a slurry. Subsequently, theprepared slurry is coated onto a base material and dried. Thereafter,the obtained stacked structure is pressed (e.g., pressing usinghydrostatic or hydraulic pressure), thereby forming the anode activematerial layer 222 on the base material. The pressing process may beomitted.

Subsequently, the stacked structure obtained by stacking the solidelectrolyte layer 230 on the anode active material layer 222 issubjected to pressing (e.g., pressing using hydrostatic or hydraulicpressure). Thereafter, the base is removed. Through this, the stackedstructure of the anode active material layer 222 and the solidelectrolyte layer 230 is fabricated.

Subsequently, metal foil including the metal layer 223, the stackedstructure of the anode active material layer 222 and the solidelectrolyte layer 230, and the cathode 210 are sequentially stacked onthe anode current collector 221 in that order. Thereafter, the obtainedstacked structure is pressed (e.g., pressing using hydrostatic orhydraulic pressure), thereby completing the manufacture of theall-solid-state secondary battery 200.

For example, the all-solid-state secondary battery 200 may be pressedduring the manufacturing operation. The pressure may be applied bysandwiching the assembled battery between two hard plates made fromstainless steel, brass, aluminum, glass, or the like, and tighteningwith screws to apply pressure. The applied pressure may be about 0.5 MPato about 10 MPa

Method of Charging All-Solid-State Secondary Battery

The method of charging the all-solid-state secondary battery 200 is thesame as that described above. That is, the all-solid-state secondarybattery 200 is charged such that the initial charge capacity of theanode active material layer 222 is exceeded. That is, the anode activematerial layer 222 is overcharged. At the initial stage of charging,lithium is incorporated into the anode active material layer 222. Whencharging is performed such that the initial charge capacity of the anodeactive material layer 222 is exceeded, lithium is deposited in the metallayer 223 (or on the metal layer 223). During discharging, lithium inthe anode active material layer 222 and the metal layer 223 (or on themetal layer 223) are ionized and transferred to the cathode 210. Thus,in the all-solid-state secondary battery 200, lithium may be used as ananode active material. In addition, the anode active material layer 222covers the metal layer 223, and thus may act as a protective layer forthe metal layer 222, and also inhibit the deposition and growth ofdendrites. This inhibits the short circuit and capacity reduction of theall-solid-state secondary battery 200, and furthermore, may enhancecharacteristics of the all-solid-state secondary battery 200. An initialcharge capacity of the all-solid-state secondary battery may be abouttwo times to about 100 times the initial charge capacity of the anodeactive material layer 222.

EXAMPLES

Hereinafter, the above-described embodiments will be described infurther detail. For the furnace black particles used below, they aredefined as follows based on particle size: furnace black powder (FB-A)particles having an average primary particle diameter D50 of about 12nm; furnace black (FB-B) particles having an average primary particlediameter D50 of about 38 nm; and furnace black (FB-C) particles havingan average particle diameter D50 of about 76 nm.

Example 1

In Example 1, an all-solid-state secondary battery was manufacturedusing the following method.

Cathode Formation

LiNi_(0.8)Co_(0.15)Mn_(0.05)O₂ (NCM) was prepared as a cathode activematerial. A Li₂O—ZrO₂ thin layer was coated on the surface of the NCMparticles using the same method described in Naoki Suzuki et al.“Synthesis and Electrochemical Properties of 14-TypeLi_(1+2x)Zn_(1−x)PS₄ Solid Electrolyte”, Chemistry of Materials, 30,2236-2244 (2018), the content of which is incorporated herein byreference. In addition, Li₆PS₅Cl, which is Argyrodite-type crystalstructure, was prepared as a solid electrolyte. In addition,polytetrafluoroethylene (Teflon binder available from DuPont) wasprepared as a binder. In addition, carbon nanofibers (CNFs) wereprepared as a conductive agent. Subsequently, these materials were mixedin a weight ratio of cathode active material:solidelectrolyte:conductive agent:binder=85:15:3:1.5, and the resultingmixture was molded into a sheet form and cut into to a square shapehaving a length of about 1.7 cm, thereby completing the fabrication of acathode sheet. In addition, the cathode sheet was pressed on Al foilhaving a thickness of 18 micrometers (μm) as a cathode current collectorto form a cathode. An initial specific charge capacity (charge capacityat the 1^(st) cycle per unit weight) of the cathode active material wasestimated to be about 240 mAh/g using a half-cell as described above.The mass of the cathode sheet was about 110 mg, corresponding to aninitial charge capacity of the cathode about 22 mAh as determined fromthe initial specific charge capacity of the cathode active materialmultiplied by the mass (g) of the cathode active material.

Anode Formation

The anode was formed by the following process.

Ni foil having a thickness of 10 μm was prepared as an anode currentcollector. In addition, furnace black powder (FB-A) having an averageprimary particle diameter D50 of about 12 nm was prepared as an anodeactive material.

Subsequently, 2 g of FB-A is put in a container, and 900 mg of anN-methyl-pyrrolidone (NMP) solution including 6.67 wt % of apolyvinylidene fluoride binder (KF-polymer #9300 manufactured by Kureha,Inc.) (3.0 wt % based on the weight of the anode) was added thereto.Then, the mixture was stirred while slowly adding a total of 20 g of NMPthereto to prepare an anode slurry. The anode slurry was coated onto Nifoil using a blade coater, and dried in air at 80° C. for 20 minutes.The obtained stacked structure was further dried under vacuum at 100° C.for 12 hours and cut into a square with a length of about 2 cm, and witha protrusion for the termination. The anode had an initial chargecapacity of about 1.2 mAh.

The ratio of initial charge capacity of the anode to initial chargecapacity of the cathode satisfies a condition of Equation 1

0.01<(b/a)<0.5  Equation 1

-   -   wherein a is the initial charge capacity of the cathode        determined from a first open circuit voltage to a maximum charge        voltage of 4.25 Volts vs. Li/Li⁺, and b is the initial charge        capacity of the anode determined from a second open circuit        voltage to 0.01 Volts vs. Li/Li⁺. For Example 1, b/a of Equation        1 was about 0.055, which satisfies the condition of Equation 1.

Formation of Solid Electrolyte Layer

A solid electrolyte layer was formed by the following process.

An acrylic binder was added to the Li₆PS₅Cl solid electrolyte to form amixture, such that the mixture included 1% by weight of the binder withrespect to the weight of the mixture. The resulting mixture was stirredwhile adding xylene and diethylbenzene thereto to prepare a slurry. Theslurry was coated onto a non-woven fabric using a blade coater, anddried in air at 40° C. The resulting stacked structure was dried in avacuum state at 40° C. for 12 hours, and cut into a square having alength of about 2.2 cm.

Manufacture of All-Solid-State Secondary Battery

The cathode, the solid electrolyte layer, and the anode were stackedtogether in this order and encapsulated in a laminating film in a vacuumstate to manufacture an all-solid-state secondary battery. In thisregard, a part of each of the cathode current collector and the anodecurrent collector was allowed to protrude to the outside from thelaminating film so as not to break the vacuum state of the battery.These protrusions were used as terminals for the cathode and the anode.In addition, the all-solid-state secondary battery was subjected tohydraulic pressure treatment at 490 megapascals (MPa) for 30 minutes.Battery characteristics are significantly enhanced by performing suchhydrostatic pressure treatment. After this treatment, theall-solid-state battery was sandwiched between two 1 cm thick stainlesssteel plates and kept pressed at 4 MPa using four screws during thecharge/discharge test.

Charge/Discharge Test

Charge/discharge characteristics of the manufactured all-solid-statesecondary battery were evaluated by the following charge/discharge test.The all-solid-state secondary battery was placed in a thermostatic bathat 60° C. At the 1st cycle, the battery was charged at a constantcurrent density of 0.5 milliamperes per square centimeter (mA/cm²) untilthe voltage reached 4.1 V, and was charged at a constant voltage of 4.1V until the current reached 0.2 millamperes (mA). Thereafter, thebattery was discharged at a constant current density of 0.5 mA/cm² untilthe voltage reached 2.0 V. After the 2^(nd) cycle, the charging processwas performed under the same conditions as that of the 1^(st) cycle ofcharging, and the discharging process was performed at a current densityof 1.67 mA/cm². The charging and discharging processes were stablyrepeated through the 17^(th) cycle. During the 18^(th) cycle ofcharging, a short circuit occurred. An initial discharge specificcapacity (discharge capacity at the 1^(st) cycle divided by the weightof the cathode active material) was 175 mAh/g, and an average cycleretention was about 99.9% per cycle. Charge/discharge characteristicswere measured and the results thereof are listed in Table 1.

The average cycle retention was obtained according to Equation 2:

Average cycle retention (%)=[(discharge capacity at the finalcycle/discharge capacity at the 2^(nd) cycle)/(total number ofcycles−2)]×100%.  Equation 2

Example 2 Observation of Cross-section Using Scanning ElectronMicroscope (SEM)

An all-solid-state secondary battery manufactured in the same manner asin Example 1 was charged only once under the same conditions as those inExample 1. Thereafter, the battery was disassembled in a dry environmentand a cross-section of the all-solid-state secondary battery waspolished using an ion milling device, and then observed using an SEM. Asillustrated in FIG. 2 , it was observed that lithium was deposited bycharging at an interface between the Ni foil and a FB-A layer.

Comparative Example 1

In the present example, Ni foil was prepared as an anode currentcollector, and this was directly used as an anode. An all-solid-statesecondary battery was manufactured in the same manner as in Example 1,except that this anode was used, and a test was performed thereon. Thatis, in Comparative Example 1, an anode active material layer was notformed on the anode current collector. An initial discharge specificcapacity was 177 mAh/g, and a short circuit occurred after three cyclesof charging. Charge/discharge characteristics were measured and theresults thereof are listed in Table 1.

Examples 3A to 3G Results Obtained After Changing Binder Amount

All-solid-state secondary batteries were manufactured in the same manneras in Example 1, except that the anodes were fabricated using anodeslurries having different amounts of binder to provide anodes having 0.3wt % to 20 wt % of binder based on the weight of the anode. Examples 3Ato 3G were prepared using seven anode slurries from mixtures including 2g of FB-A and 90 mg (0.3 wt %), 150 mg (0.5 wt %), 300 mg (1 wt %), 1.5g (5 wt %), 3 g (10 wt %), 4.5 g (15 wt %), or 6 g (20 wt %),respectively, of the NMP solution including 6.67 wt % of binder fromExample 1.

All-solid-state secondary batteries were manufactured in the same manneras in Example 1, except that anodes were fabricated using theseslurries. The initial charge capacities of the anodes of each of theall-solid-state secondary batteries were about 1.2 mAh to about 1.8 mAh,which satisfy the condition of Equation 1. Charge/dischargecharacteristics were measured using the same method as that used inExample 1. The results thereof are listed in Table 1. From theseresults, it can be seen that when the amount of the binder ranges from0.3 wt % to 15 wt % with respect to the weight of the anode,short-circuit inhibitory effects may be obtained. However, when theamount of the binder is 0.3 wt %, characteristics such as averagecapacity retention and total number of cycles deteriorated, and theformed film weakened such that handling thereof was difficult. When theamount of the binder is 20 wt %, lithium does not satisfactorilypermeate the FB-A film during charging and a short circuit occurred atthe 2^(nd) cycle.

TABLE 1 Initial Initial Initial Cathode Anode Discharge Anode ChargeCharge Specific Capacity Total Binder Capacity (a) Capacity (b) CapacityRetention Cycles [wt %] [mAh] [mAh] b/a [mAh/g] [%/cycle] [n] Example 13.0% 22 1.2 0.055 175 99.9 17 Example 3A 0.3% 22 1.2 0.055 174 83.1 6Example 3B 0.5% 22 1.8 0.082 173 99.4 20 Example 3C 1.0% 22 1.8 0.082176 99.9 23 Example 3D 5.0% 22 1.8 0.082 170 99.4 33 Example 3E 10.0% 221.8 0.082 160 99.5 30 Example 3F 15.0% 22 1.8 0.082 156 95.4 5 Example3G 20.0% 22 1.8 0.082 150 — 1 Comparative — 22 0.0 0.000 177 — 2 Example1

Examples 4A to 4E

An anode was formed using the following process.

In the present example, water was used as a solvent for preparing ananode slurry and styrene butadiene rubber (SBR) was used as a binder(ZEON BM-451B). 20 mg of carboxymethylcellulose and 5 g of water wereadded to 2 g of FB-A. Subsequently, the mixture was stirred while slowlyadding 10 g of water thereto, and finally, an amount of an aqueoussolution including 40 wt % of SBR binder was added to the resultingsolution, followed by stirring, to prepare an anode slurry. The amountsof the aqueous SBR binder solution in Examples 4A to 4E were 133 mg (3wt %), 250 mg (5 wt %), 500 mg (10 wt %), 750 mg (15 wt %), and 1 g (20wt %), respectively, where the weight percent of the SBR binder is basedon the weight of the anode. Each of these five anode slurries was coatedonto Ni foil using a blade coater, and dried in air at 80° C. for 20minutes. The resulting stacked structure was further dried at 145° C.for 12 hours. The initial charge capacities of the anodes were about 1.2mAh, which satisfies the condition of Equation 1.

All-solid-state secondary batteries were manufactured in the same manneras in Example 1, except that these anodes were used, andcharge/discharge characteristics were measured using the same method asthat used in Example 1. The results thereof are listed in Table 2 below.From these results, it can be seen that when the amount of the binderranges from 3 wt % to 15 wt % with respect to the anode, short-circuitinhibitory effects may be obtained. When the amount of the binder was 20wt %, lithium does not permeate the FB-A film during charging, and ashort circuit occurred at the 2^(nd) cycle.

Examples 5A and 5B

In the present example, Ni foil having a thickness of 10 μm was preparedas an anode current collector. A gold (Au) thin film having a thicknessof about 20 nm (Example 5A) or about 100 nm (Example 5B) were formed onthe Ni foil using a DC sputtering device. The anode slurry preparedaccording to Example 1 was coated onto each of the Au thin films to formtwo different anodes. An initial charge capacity of each anode was about1.2 mAh. Thus, b/a of Equation 1 was 0.055, which satisfies thecondition of Equation 1.

All-solid-state secondary batteries were manufactured in the same manneras in Example 1, except that these anode were used, and charge/dischargecharacteristics were measured using the same method as that used inExample 1. The results thereof are shown in Table 2. From these results,it was confirmed that a short circuit inhibitory effect was enhanced dueto the formation of the Au thin films on the current collector.

Example 6

In the present example, Ni foil having a thickness of 10 μm was preparedas an anode current collector. A tin (Sn) plating layer was formed onthe Ni foil. The thickness of the Sn plating layer was about 500 nm. Theanode slurry prepared according to Example 1 was coated onto the Sn thinfilm of the Ni foil to form an anode. An initial charge capacity of theanode was about 1.4 mAh. Thus, b/a of Equation 1 is 0.064, whichsatisfies the condition of Equation 1.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1, except that this anode was used, and charge/dischargecharacteristics were measured using the same method as that used inExample 1. The results, as provided in Table 2, showed that charging anddischarging were stably performed to the 100^(th) cycle or more. Theterm “or more” as used herein means that a short circuit did not occurup to 100^(th) cycle, and thus a cycle testing was stopped.

TABLE 2 Initial Initial Initial Cathode Anode Discharge Anode ChargeCharge Specific Capacity Total Binder Capacity (a) Capacity (b) CapacityRetention Cycles [wt %] [mAh] [mAh] b/a [mAh/g] [%/cycle] [n] Example 4A3.0% 22 1.2 0.055 165 99.1 6 Example 4B 5.0% 22 1.2 0.055 161 99.4 79Example 4C 10.0% 22 1.2 0.055 171 99.6 59 Example 4D 15.0% 22 1.2 0.055165 99.1 15 Example 4E 20.0% 22 1.2 0.055 156 — 1 Example 5A 1.0% 22 1.20.055 172 99.6 39 Example 5B 1.0% 22 1.2 0.055 173 99.7 65 Example 63.0% 22 1.4 0.064 150 99.7 >100

Example 7A

In the present example, acetylene black (AB) having an average primaryparticle diameter D50 of about 35 nm was used as an anode activematerial. First, 2 g of AB active material was put into a container, andthen 900 mg of an NMP solution including 6.67 wt % of a binder(KF-polymer #9300 available from Kureha Inc.) was added thereto.Subsequently, the mixture was stirred while slowly adding NMP thereto toprepare an anode slurry. NMP was added until the viscosity of the anodeslurry became a state suitable for film formation using a blade coater.The prepared anode slurry was coated onto Ni foil using a blade coater,and dried in air at 80° C. for 20 minutes. The resulting stackedstructure was then dried under vacuum at 100° C. for 12 hours. An anodeincluding AB was formed by the above-described processes.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1, except that the anode including AB was used, andcharge/discharge characteristics were measured using the same method asthat used in Example 1. The results thereof are listed on Table 3 below.Charging and discharging processes were stably performed up to the100^(th) cycle or more for the case of the all-solid-state secondarybattery including the AB anode.

Example 7B

In the present example, Ketjen black (KB) having an average primaryparticle diameter D50 of about 39.5 nm was used as an anode activematerial. First, 2 g of KB active material was put into a container, andthen 300 mg of an NMP solution including 6.67 wt % of a binder(KF-polymer #9300 available from Kureha Inc.) was added thereto.Subsequently, the mixture was stirred while slowly adding NMP thereto toprepare an anode slurry. NMP was added until the viscosity of the anodeslurry became a state suitable for film formation using a blade coater.The prepared anode slurry was coated onto Ni foil using a blade coater,and dried in air at 80° C. for 20 minutes. The resulting stackedstructure was then dried under vacuum at 100° C. for 12 hours. An anodeincluding KB was formed by the above-described processes.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1, except that the anode including KB was used, andcharge/discharge characteristics were measured using the same method asthat used in Example 1. The results thereof are listed on Table 3 below.Charging and discharging processes were stably performed up to the 40thcycle or more for the case of the all-solid-state secondary batteryincluding the KB anode.

Examples 8A to 8D Reviews on Thickness of Anode Active Material Layer

In the present example, Examples 8A to 8D included films having athickness of 1.5 μm, 6 μm, 12 μm, and 18 μm, respectively, that wereformed using AB as an anode active material, and each film was used asan anode. All-solid-state secondary batteries were manufactured in thesame manner as in Example 7A, except that these anodes were used, andcharge/discharge characteristics were measured using the same method asthat used in Example 1. The results thereof were listed in Table 3below. In the case in which the thickness of the anode was 1.5 μm, ashort circuit inhibitory effect was shown. In addition, although it wasconfirmed that cycle lifespan was extended when the thickness of theanode was greater, specific charge capacity at the 2^(nd) cycledecreased, i.e., from greater than about 150 mAh/g to about 140 mAh/gwhen the thickness of the anode was about 18 μm. This indicates that asthe thickness of the film increases, the anode has an increasedresistance, resulting in deterioration of output characteristics.

Comparative Examples 2A and 2B

In the present examples, all-solid-state secondary batteries weremanufactured in the same manner as in Example 6, except that powder-typespherical graphite particles having an average primary particle diameterD50 of about 15 μm (Comparative Example 2A) or powder-type scalygraphite particles having an average primary particle diameter D50 ofabout 5 μm (Comparative Example 2B) were used as anode active materials,and a test was performed thereon. The results thereof are shown in Table3 below. In both cases, a short circuit occurred during the 2^(nd) cycleof charging.

Comparative Examples 3A and 3B Observation of Cross-Section Using SEM

In the present examples, all-solid-state secondary batteries weremanufactured in the same manner as in Comparative Examples 2A and 2Busing the spherical graphite (Comparative Example 3A) or the scalygraphite (Comparative Example 3B) as an anode active material. Eachbattery was charged once under the same conditions as those in Example2. Subsequently, the batteries were disassembled in a dry air atmosphereand the cross-sections of the all-solid-state secondary batteries wereeach polished using an ion milling device, and then observed using aSEM. As illustrated in FIG. 5 , in both batteries it was observed thatlithium was deposited by charging at an interface between a graphitelayer and a solid electrolyte layer.

Example 9

In the present example, LiNi_(0.8)Co_(0.15)Al_(0.05)O₂(NCA) was used asa cathode active material. The cathode was prepared in the same manneras Example 1. The initial charge capacity of the cathode layer was about22 mAh using the half-cell as described above.

The anode included a lithium metal layer arranged between Ni foil as ananode current collector and a furnace black (FB-B) layer using FB-Bhaving an average primary particle diameter D50 of about 38 nm as ananode active material. The FB-B particles are an amorphous carbonmaterial.

An anode precursor was prepared as follows. First, an FB-B film wasformed on Ni foil using the same method as that used in Example 1. Aninitial charge capacity of the anode precursor including the FB-B filmwas 2.4 mAh. The resulting b/a value of the battery is 0.109, whichsatisfies the condition of Equation 1. Next, the NCA cathode formed inthe same manner as in Example 1, and the solid electrolyte layer wasformed according to the method of Example 1.

The all-solid-state secondary battery was prepared as follows. The anodeprecursor including the Ni foil with the FB-B layer formed thereon werestacked on the solid electrolyte layer, having the shape of a squarewith a side length of 2.2 cm, such that the side having the FB-B layercontacted the solid electrolyte layer. The resulting structure wasencapsulated in a laminating film in a vacuum state and subjected tohydraulic pressure treatment at 490 MPa for 30 minutes. After treatment,the laminating film was disassembled and the Ni foil was removed fromthe FB-B layer, wherein the FB-B film was effectively transferred ontothe solid electrolyte layer. Next, Li foil in the shape of a square witha side length of 2 cm and having a thickness of 30 μm was pressed ontothe Ni foil, the resulting structure was stacked on the above-describedstacked structure including the FB-B film and the solid electrolytelayer such that the Li foil comes into contact with the FB-B film,thereby forming a stacked structure including the anode and theelectrolyte layer.

The cathode was then stacked on the electrolyte layer to provide astacked structure that included the cathode, solid electrolyte layer,and anode in this order, followed by encapsulation in a laminating filmin a vacuum state, thereby completing the manufacture of anall-solid-state secondary battery. In this regard, a part of each of thecathode current collector and the anode current collector was allowed toprotrude to the outside from the laminating film so as not to break thevacuum state of the battery. These protrusions were used as terminalsfor the cathode and the anode. In addition, the all-solid-statesecondary battery was subjected to hydrostatic pressure treatment at 49MPa for 5 minutes. After this treatment, the all-solid-state battery wassandwiched between two 1 cm thick stainless steel plates and keptpressed at 4 MPa using four screws during the charge/discharge test.

Next, the battery was evaluated by a charge/discharge test and theresults thereof are shown in Table 3 below. At the 1^(st) cycle, thebattery was charged at a constant current density of 0.5 mA/cm² untilthe voltage reached 4.2 V, and was charged at a constant voltage of 4.2V until the current reached 0.2 mA. Thereafter, the battery wasdischarged at a constant current density of 0.5 mA/cm² until the voltagereached 2.0 V. After the 2^(nd) cycle, the battery was charged at aconstant current density of 1.67 mA/cm² until the battery voltagereached 4.2 V, and charged at a constant voltage of 4.2 V until thecurrent reached 0.2 mA/cm². The discharging process was performed at acurrent density of 2.5 mA/cm². The charge/discharge test was performedafter the all-solid-state secondary battery was placed in a thermostaticbath at 60° C. As a result, the charging and discharging processes werestably performed up to 190^(th) cycle or more. An initial specificdischarge capacity was 218 mAh/g and a capacity retention was 99.95% percycle, as determined according to Equation 2.

TABLE 3 Initial Initial Initial Cathode Anode Discharge Anode ChargeCharge Specific Capacity Total Binder Capacity (a) Capacity (b) CapacityRetention Cycles [wt %] [mAh] [mAh] b/a [mAh/g] [%/cycle] [n] Example 7A3.0% 22 3.6 0.164 168 99.7 >100 Example 7B 1.0% 22 1.2 0.055 16399.5 >40 Example 8A 3.0% 22 0.3 0.014 154 99.5 25 Example 8B 3.0% 22 1.20.055 170 99.5 21 Example 8C 3.0% 22 2.4 0.109 169 99.4 >100 Example 8D3.0% 22 3.6 0.164 168 99.7 >100 Example 9 3.0% 22 2.4 0.109 21899.95 >100 Comparative 3.0% 22 2.0 0.091 165 — 1 Example 2A Comparative3.0% 22 1.0 0.045 162 — 1 Example 2B Comparative 0 22 0 0 206 — 1Example 4

Comparative Example 4

In the present example, the anode was prepared in the same manner asExample 9, except the process of transferring a FB-B layer to a solidelectrolyte layer was omitted. The cathode formed according to Example 9and the solid electrolyte layer formed according to Example 1 werestacked, and encapsulated in a laminating film in a vacuum state,followed by hydraulic pressure treatment at 490 MPa for 30 minutes.After treatment, the laminating film was disassembled and the stackedstructure was taken out thereof. A Li foil in the shape of a square witha length of 2 cm and having a thickness of 30 μm was pressed onto Nifoil, the resulting structure was stacked on the above-described stackedstructure such that the Li foil came into contact with the solidelectrolyte layer, followed by encapsulation in a laminating film in avacuum state, thereby completing the manufacture of an all-solid-statesecondary battery. In this regard, a part of each of the cathode currentcollector and the anode current collector were allowed to protrude tothe outside from the laminating film so as not to break the vacuum stateof the battery. These protrusions were used as terminals for the cathodeand the anode. In addition, the all-solid-state secondary battery wassubjected to hydrostatic pressure treatment at 49 MPa for 5 minutes.After this treatment, the all-solid-state battery was sandwiched betweentwo 1 cm thick stainless steel plates and kept pressed at 4 MPa usingfour screws during the charge/discharge test.

A charge/discharge test was performed on the all-solid-state secondarybattery under the same conditions as those in Example 9. An initialspecific discharge capacity was 206 mAh/g, and a short circuit occurredduring the 2^(nd) cycle of charging. The results are shown in Table 3above.

Examples 10A to 10E

In the present example, NCM cathode was used as cathode active material,and silicon powder having an average particle diameter D50 of 100 nm(Example 10A), silver powder having an average particle diameter D50 of3 μm (Example 10B), tin powder having an average particle diameter D50of 150 nm (Example 10C), aluminum powder having an average particlediameter D50 of 3 μm (Example 10D), or bismuth powder having an averageparticle diameter D50 of 1.5 μm (Example 10E) were each used as anodeactive materials.

The anodes were prepared as follows. First, 4 g of each anode activematerial was put in a container, and 4 g of an NMP solution including 5wt % of a binder (KF-polymer #9300 available from Kureha Inc.) was addedthereto. Subsequently, the mixed solution was stirred while slowlyadding NMP thereto to prepare an anode slurry. NMP was added until theviscosity of the anode slurry became a state suitable for film formationusing a blade coater. The prepared anode slurry was coated onto Ni foilusing a blade coater, and dried in air at 80° C. for 20 minutes. Theresulting stacked structure was further dried in a vacuum state at 100°C. for 12 hours.

All-solid-state secondary batteries using each of the anodes weremanufactured in the same manner as in Example 1. At the 1^(st) cycle,each battery was charged at a constant current density of 0.5 mA/cm²until the battery voltage reached 4.2 V, and then was charged at aconstant voltage of 4.2 V until the current reached 0.2 mA. Thereafter,each battery was discharged at a constant current density of 0.5 mA/cm²until the battery voltage reached 2.0 V. After the 2^(nd) cycle, eachbattery was charged at a constant current density of 2.5 mA/cm² untilthe battery voltage reached 4.2 V, and then discharged at a constantcurrent density of 2.5 mA/cm². A charge/discharge test was performedusing the same method as that used in Example after each all-solid-statesecondary battery was placed in a thermostatic bath at 60° C. Theresults thereof are shown in Table 4 below. In all of the batteriesincluding the different anodes, an effect of inhibiting a short circuitduring charging was confirmed. In addition, it was confirmed that ashort circuit inhibitory effect was shown also in the case of theparticle diameter of 3 μm (i.e., Examples 10B and 10D).

Comparative Examples 5A and 5B

In the present example, all-solid-state secondary batteries weremanufactured in the same manner as in Example 1, except that nickelparticles having average particle diameters D50 of 100 nm (ComparativeExample 5A) or silicon carbide particles having particle diameters D50of 50 nm (Comparative Example 5B) were used as anode active materials.These anode active materials do not provide anodes that have ameasurable charge capacity, and thus the b/a value is 0, which does notsatisfy the condition of Equation 1. Charge/discharge characteristics ofeach battery were evaluated using the same method as that used inExample 10. The results thereof are shown in Table 4 below, from whichit was confirmed that a short circuit occurred during the 1^(st) cycleof charging.

Comparative Examples 6A and 6B

Mixing of Element Alloyable with Li and Element not Alloyable with Li

In the present example, silicon particles having average particlediameters D50 of 100 nm, nickel particles having average particlediameters D50 of 100 nm, and silicon carbide particles having averageparticle diameters D50 of 50 nm were prepared. Anode active materialswere prepared using a mixture of silicon and nickel particles in aweight ratio of 1:1 (Comparative Example 6A) or a mixture of silicon andsilicon carbide particles in a weight ratio of 1:1 were prepared(Comparative Example 6B). All-solid-state secondary batteries weremanufactured in the same manner as in Example 10, except that theseanode active material mixtures were used as anode active materials. Theb/a value of each all-solid-state secondary battery satisfied thecondition of Equation 1.

Charge/discharge characteristics of each all-solid-state secondarybattery was evaluated using the same method as that used in Example 10.The results thereof are shown in Table 4. In both cases, an effect ofinhibiting a short circuit during charging was small.

TABLE 4 Initial Initial Initial Cathode Anode Discharge Anode ParticleCharge Charge Specific Capacity Total Active Diameter Capacity (a)Capacity (b) Capacity Retention Cycles Material (μm) [mAh] [mAh] b/a[mAh/g] [%/cycle] [n] Example Si 0.1 22 6 0.27 192 99.7 18 10A ExampleAg 3 22 1.5 0.07 187 99.8 >60 10B Example Sn 0.2 22 4.7 0.21 17899.7 >60 10C Example Al 3 22 3.0 0.14 157 99.7 >60 10D Example Bi 1.5 223.0 0.136 171 99.7 >60 10E Comparative Ni 0.1 22 0 0 160 — 0 Example 5AComparative SiC 0.05 22 0 0 156 — 0 Example 5B Comparative Si/Ni — 223.4 0.15 187 99.5 3 Example 6A Comparative Si/SiC — 22 3.9 0.18 187 99.54 Example 6B

Examples 1A and 11B

In the present examples, NCA cathode was used as cathode activematerial, furnace black (FB-C) particles having an average particlediameter D50 of about 76 nm and silver particles having an averageparticle diameter D50 of about 800 nm were prepared for the anode. Anodeactive materials prepared using the FB-C powder alone (Example 11A) or amixture of FB-C and silver particles in a weight ratio of 3:1 (Example11B) were used in the respective anodes. The FB-C particles are anamorphous carbon material.

The anodes were prepared as follows. First, 4 g of the anode activematerial was put in a container, and 4 g of an NMP solution including 5wt % of a binder (KF-polymer #9300 available from Kureha Inc.) was addedthereto. Subsequently, the mixed solution was stirred while slowlyadding NMP thereto to prepare an anode slurry. NMP was added until theviscosity of the anode slurry became a state suitable for film formationusing a blade coater. The prepared anode slurry was coated onto Ni foilusing a blade coater, and dried in air at 80° C. for 20 minutes. Theresulting stacked structure was further dried in a vacuum state at 100°C. for 12 hours. An anode was formed by the above-described process foreach of the anode active materials.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1 using each of these anodes. Each battery was evaluatedby the following charge/discharge test. At the 1^(st) cycle, eachbattery was charged at a constant current density of 0.5 mA/cm² untilthe battery voltage reached an upper limit of 4.25 V, and was charged ata constant voltage of 4.25 V until the current reached 0.2 mA.Thereafter, each battery was discharged at a constant current density of0.5 mA/cm² until the battery voltage reached 2.0 V. After the 2^(nd)cycle, each battery was charged at a constant current density of 2.5mA/cm² until the battery voltage reached 4.25 V, and then discharged ata constant current density of 2.5 mA/cm². A charge/discharge test wasperformed using the same method as in Example 1 after eachall-solid-state secondary battery was placed in a thermostatic bath at60° C. The results thereof are shown in Table 5. In the case in whichFB-C was used alone as the anode active material, charging anddischarging were performed only up to the 13th cycle. In the case of theanode active material including the mixture of FB-C and silver, chargingand discharging were stably performed up to the 100^(th) cycle or more.In addition, an initial discharge capacity was increased, from which itcan be seen that characteristics are enhanced using the anode activematerial mixture of FB-C powder and silver particles (FB-C/Ag).

Examples 11C to 11E

In the present examples, furnace black (FB-B) particles having anaverage particle diameter D50 of about 38 nm and silver particles havingan average particle diameter D50 of about 20 nm, 60 nm, or 800 nm wereprepared. Anode active materials prepared using the FB-B powder alone(Example 11F) or a mixture of FB-B and silver particles in a weightratio of 3:1 (Examples 11C to 11E) were used in the respective anodes.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1 using each of these anodes. A charge/discharge test wasperformed using the same method as in Example 11A after eachall-solid-state secondary battery was placed in a thermostatic bath at60° C. The results thereof are shown in Table 5. In the case in whichFB-B was used alone as the anode active material, charging anddischarging were performed only up to the second cycle. In the case ofthe anode active material including the mixture of FB-B and silver,charging and discharging were stably performed up to the 100^(th) cycleor more. In addition, an initial discharge capacity was increased, fromwhich it can be seen that characteristics are enhanced using the anodeactive material mixture of FB-B powder and silver particles (FB-B/Ag).The capacity retention was better when the Ag particle size is less than100 nm.

Examples 11F to 11L

In the present example, furnace black (FB-B) particles having an averageparticle diameter D50 of about 38 nm and silver particles having anaverage particle diameter D50 of about 60 nm were prepared. The anodeactive materials having different weight ratios of FB-B to silverparticles, as specified in Table 5, were used for respective anodes.

An all-solid-state secondary battery was manufactured in the same manneras in Example 1 using each of these anodes. A charge/discharge test wasperformed using the same method as in Example 11A after eachall-solid-state secondary battery was placed in a thermostatic bath at60° C. The results thereof are shown in Table 5. By adding Ag particlesfrom 5 wt % to 67 wt % based on the total weight of the anode activematerial, the capacity and the cycle retention were improved relative toExample 11F which contained no silver particles.

TABLE 5 Initial Initial Initial Cathode Anode Discharge Anode ParticleCharge Charge Specific Total Active Diameter Capacity (a) Capacity (b)Capacity Cycles Material (μm) [mAh] [mAh] b/a [mAh/g] [n] Example 11AFB-C 0.076 22 2.1 0.095 201 13 Example 11B FB-C/Ag 0.8 22 2.4 0.109219 >100 (3:1) (Ag) Example 11C FB-B/Ag 0.02 26 2.4 0.092 213 >100 (3:1)(Ag) Example 11D FB-B/Ag 0.06 26 2.4 0.092 212 >100 (3:1) (Ag) Example11E FB-B/Ag 0.8 26 2.4 0.092 210 >100 (3:1) (Ag) Example 11F FB-B 0.03826 2.4 0.092 204 2 Example 11G FB-B/Ag 0.06 26 2.4 0.092 211 17 (19:1)(Ag) Example 11H FB-B/Ag 0.06 26 2.4 0.092 223 >100 (7:1) (Ag) Example11I FB-B/Ag 0.06 26 2.4 0.092 223 >100 (3:1) (Ag) Example 11J FB-B/Ag0.06 26 2.4 0.092 218 >100 (2:1) (Ag) Example 11K FB-B/Ag 0.06 26 2.40.092 224 >100 (1:1) (Ag) Example 11L FB-B/Ag 0.06 26 2.4 0.092 211 >100(1:2) (Ag)

Examples 12A to 12E

In the present example, FB-C powder (Example 12A) or powder mixturesprepared by mixing FB-C with 10 wt % (Example 12B), 25 wt % (Example12C), 33 wt % (Example 12D), or 50 wt % (Example 12E) of silverparticles having an average particle diameter D50 of about 800 nm wereprepared as anode active materials. An anode was formed using the samemethod as that used in Example 11A by using each anode active materialpowder, followed by manufacture of an all-solid-state secondary batteryusing the same method as that used in Example 11 A.

Output characteristics of these all-solid-state secondary batteries wereevaluated by the following charge/discharge test. At the 1^(st) cycle,each battery was charged at a constant current density of 0.5 mA/cm²until the battery voltage reached an upper limit of 4.25 V, and wascharged at a constant voltage of 4.25 V until the current reached 0.2mA. Thereafter, each battery was discharged at a constant currentdensity of 0.5 mA/cm² until the battery voltage reached 2.0 V. At the2^(nd) cycle and the 3^(rd) cycle, charging was performed under the sameconditions as those at the 1^(st) cycle, and then each battery wasdischarged at a constant current density of 1.67 mA/cm² (2^(nd) cycle)or 5 mA/cm² (3^(rd) cycle) until the voltage reached 2 V. Acharge/discharge test was performed using the same method as used inExample 1 after each all-solid-state secondary battery was placed in athermostatic bath at 60° C. The results thereof are shown as a graph inFIG. 6 , from which it can be confirmed that capacity and dischargecharacteristics at a high current density may be enhanced using theanode active material including a mixture of FB-C and silver particles.

Examples 13a to 13E

In the present example, powders prepared by mixing FB with 25 wt %(Example 13A), 33 wt % (Example 13B), or 50 wt % (Example 13C) ofsilicon particles having an average particle diameter D50 of about 100nm, a powder mixture of FB-C and 25 wt % of Sn particles having anaverage particle diameter D50 of 150 nm (Example 13D), or a powermixture of FB-C and 25 wt % of Zn particles having an average particlediameter D50 of 100 nm (Example 13E) were prepared as anode activematerials. An anode was formed using the same method as that used inExample 11 using each anode active material powder, an all-solid-statesecondary battery was manufactured using the same method as that used inExample 11A, and output characteristics thereof were evaluated using thesame method as that used in Example 12A. The results thereof are shownas a graph in FIG. 7 , from which it can be seen that capacity anddischarge characteristics at a high current density may be enhancedusing an anode active material mixture of FB-C and Si particles, Znparticles, or Sn particles.

FIG. 8 illustrates perspective views for explaining an all-solid-statesecondary battery according to an embodiment and a method of chargingthe same according to another embodiment.

Referring to FIG. 8 , the all-solid-state secondary battery may includean anode current collector 310, an anode active material layer 320, asolid electrolyte layer 400, a cathode active material layer 520, and acathode current collector 510. In this regard, the anode active materiallayer 320 may include a carbon black material. At the initial stage orafter discharging, lithium may be not present or substantially notpresent between the anode current collector 310 and the anode activematerial layer 320. During charging, lithium is deposited between theanode current collector 310 and the anode active material layer 320 anda metal layer 330 may be formed by such lithium. In this case, the anodeactive material layer 320 may act as a protective layer. A ratio ofinitial charge capacity (b) of the anode active material layer 320 toinitial charge capacity (a) of the cathode active material layer 520 maysatisfy the following condition: 0.01<(b/a)<0.5. In addition, the anodeactive material layer 320 may further include particles of a metal or asemiconductor in a carbon black material layer. In this regard, themetal or the semiconductor may be, for example, gold (Au), platinum(Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth(Bi), tin (Sn), zinc (Zn), or a combination thereof. Through this, thecharacteristics of an anode may be further enhanced. Instead of usingthe carbon black, for example, furnace black (FB), acetylene black (AB),Ketjen black (KB), graphene, a combination thereof, or the like may beused. In an embodiment, before charging, a metal layer may be previouslyformed between the anode current collector 310 and the anode activematerial layer 320.

FIG. 9 is a graph showing charge/discharge characteristics of anexemplary all-solid-state secondary battery according to an embodiment.

Referring to FIG. 9 , charge/discharge characteristics of anall-solid-state secondary battery (lithium battery) were evaluated.Characteristics evaluation was performed after the all-solid-statesecondary battery was placed in a thermostatic bath at 60° C. At the1^(st) cycle, the battery was charged at a constant current density of0.5 mA/cm² until the battery voltage reached 4.25 V, and was charged ata constant voltage of 4.25 V until the charge current reached 0.2 mA.Thereafter, the battery was discharged at a constant current density of0.5 mA/cm² until the battery voltage reached 2.0 V. After the 2^(nd)cycle, the battery was subjected to constant-current charging andconstant-current discharging at a current density of 1.67 mA/cm² and 2.5mA/cm², respectively. As illustrated in charge/discharge curves of FIG.9 , stable charging and discharging were possible up to the 100^(th)cycle or more, an initial discharge capacity was 219 mAh/g of activematerial, and an average capacity retention was about 99.9% per cycle.

Examples 14a to 14C

In the present example, powders prepared using KB-B and platinumparticles were used as anode active materials. The platinum was presentin amounts of 0 wt %, 20 wt %, or 50 wt % based on the total weight ofthe anode active material in Examples 14A, 14B, and 14C, respectively.The anodes layers were prepared as follows. First, 1 g of the anodemixture (powder) active material was put in a container, and 4 g of anNMP solution including 5 wt % of a binder (#9300KF-polymer #9300available from Kureha Inc.) was added thereto. Subsequently, the mixturewas stirred while slowly adding NMP thereto to prepare an anode slurry.NMP was added until the viscosity of the anode slurry became a statesuitable for film formation using a blade coater. The prepared anodeslurry was coated onto Ni foil using a blade coater, and dried in air at80° C. for 20 minutes. The resulting stacked structure was further driedin a vacuum state at 100° C. for 12 hours. An anode layer was formed bythe above-described process for each of the anode active materials. Theall-solid batteries using these anodes are fabricated in the same way asExample 11A. The discharge properties were evaluated in the same way asExample 12A.

FIG. 10 is a graph showing the change is discharge specific capacitybased on current density for Examples 14A (“KB”), 14B (“Pt20%”), and 14C(“Pt50%”). These results demonstrate that the discharge properties areimproved by the addition of Pt particles to the anode active material.

Although particular embodiments have been described in the foregoingdescription, these are exemplary embodiments and are not intended tolimit the scope of the present disclosure, but are construed as beingprovided for illustrative purposes. For example, it will be understoodby those of ordinary skill in the art that the all-solid-state secondarybattery and the method of charging the same that have been describedwith reference to FIGS. 1 to 10 may be in various different forms. Thus,the scope of the present disclosure is not limited by theabove-described embodiments, but should be defined by the technicalscope and spirit of the following claims.

What is claimed is:
 1. An all-solid-state secondary battery comprising:a cathode comprising a cathode active material layer, the cathode activematerial layer comprises a cathode active material and a solidelectrolyte; an anode comprising an anode current collector, and ananode active material layer on the anode current collector, wherein theanode active material layer comprises an anode active materialcomprising amorphous carbon, and a binder, wherein the anode activematerial layer has a thickness of about 1 micrometer to about 20micrometers; and a solid electrolyte layer between the cathode and theanode.
 2. The all-solid-state secondary battery of claim 1, wherein aratio of an initial charge capacity of the anode active material layerto an initial charge capacity of the cathode active material layersatisfies Equation 1:0.01<(b/a)<0.5  Equation 1 wherein a is the initial charge capacity ofthe cathode active material layer, determined from a first open circuitvoltage to a maximum charging voltage vs. Li/Li⁺, and wherein b is theinitial charge capacity of the anode active material layer, determinedfrom a second open circuit voltage to 0.01 Volts vs. Li/Li⁺.
 3. Theall-solid-state secondary battery of claim 1, wherein the anode activematerial is in a form of a particle, wherein the anode active materialhas an average particle diameter of about 4 micrometers or less.
 4. Theall-solid-state secondary battery of claim 1, wherein the amorphouscarbon comprises at least one of furnace black, acetylene black, Ketjenblack, or graphene, and has an average particle diameter D50 of about 4micrometers or less.
 5. The all-solid-state secondary battery of claim1, wherein the anode active material further comprises at least one ofgold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, orzinc.
 6. The all-solid-state secondary battery of claim 5, wherein theanode active material comprises a mixture of a first particle comprisingthe amorphous carbon and a second particle comprising the at least oneof gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin,or zinc, and wherein an amount of the second particle is about 8 weightpercent to about 60 weight percent, based on a total weight of themixture.
 7. The all-solid-state secondary battery of claim 6, wherein aweight ratio of the amorphous carbon to the second particle is about10:1 to about 1:2.
 8. The all-solid-state secondary battery of claim 1,wherein the binder comprises at least one of styrene butadiene rubber,polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene, andan amount of the binder ranges from about 0.3 weight percent to about 15weight percent, based on a total weight of the anode active material. 9.The all-solid-state secondary battery of claim 1, further comprising ametal layer between the anode active material layer and the anodecurrent collector, wherein the metal layer comprises at least one oflithium or a lithium alloy.
 10. The all-solid-state secondary battery ofclaim 9, wherein the metal layer is disposed within the anode activematerial layer, between the anode active material layer and the anodecurrent collector, or both, and the metal layer has a thickness of about1 micrometer to about 200 micrometers.
 11. The all-solid-state secondarybattery of claim 1, further comprising a plating layer on the anodecurrent collector and between the anode current collector and the anodeactive material layer, the plating layer comprising an element alloyablewith lithium, wherein the plating layer comprises at least one of gold,silver, zinc, tin, indium, silicon, aluminum, or bismuth, and has athickness of about 1 nanometer to about 500 nanometers.
 12. Theall-solid-state secondary battery of claim 1, wherein the anode currentcollector, the anode active material layer, and a region therebetweenare Li-free regions at an initial state of or after discharge of theall-solid-state secondary battery.
 13. The all-solid-state secondarybattery of claim 1, wherein the solid electrolyte layer comprises asolid electrolyte, and the solid electrolyte of the solid electrolytelayer is amorphous, crystalline, or in a mixed form.
 14. Theall-solid-state secondary battery of claim 1, wherein theall-solid-state secondary battery is a lithium battery, and the maximumcharging voltage is about 3 volts to about 5 volts versus Li/Li⁺. 15.The all-solid-state secondary battery of claim 1, wherein the anodecurrent collector comprises a material that does not form a compoundwith lithium.
 16. The all-solid-state secondary battery of claim 15,wherein the anode current collector comprises at least one of titanium,copper, iron, cobalt, or nickel.
 17. A method of charging anall-solid-state secondary battery, the method comprising: charging theall-solid-state secondary battery of claim 1, wherein an initial chargecapacity of the anode active material layer is exceeded, a metal layeris formed between the anode active material layer and the anode currentcollector during the charging of the all-solid-state secondary battery,and the metal layer comprises at least one of lithium or a lithiumalloy.
 18. The method of claim 17, wherein a charge capacity of theall-solid-state secondary battery is about two times to about 100 timesgreater than an initial charge capacity of the anode active materiallayer.
 19. The method of claim 17, wherein when the initial chargecapacity of the anode active material layer is exceeded, a content oflithium in the metal layer comprising at least one of lithium or alithium alloy is increased.
 20. The method of claim 19, wherein themetal layer is disposed within the anode active material layer, betweenthe anode active material layer and the anode current collector, orboth.